Arrangement for supply of current to electrothermic melting furnaces



Dec. 11, 1934, |NGEL5RUD ARRANGEMENT FOR SUPPLY OF CURRENT T0 Ell-EGTROTHERMIG MELTING FURNACES Filed Feb. 13, 1932 Patented 11, 1934ARRANGEMENT FOR SU-PPLY OF CURRENT TO ELECTROTHERMIC MELTING FUR- NACESHildor Ingelsrud, Oslo,

Norske Aktleselskab fo Oslo, Norway Norway, assignor to Bet rElektrokemisk Industri,

Applicatilfii February 13,4932, Serial No. 592,855

g In Norway February 13, 1931 4 Claims.

As the inductive'voltage drop in a conductor is approximatelyproportional to the amperage, the arrangement of the supply leads to theelectrodes becomes a matter of the greatest importance.

The big melting furnaces are most frequently three-phase furnaces andthe transformers supplying current to such furnaces are on the primaryside generally delta connected and on the secondary side either star ordelta connected. By delta connecting the secondary side a favourablearrangement of the leads is obtained by taking the lead and return barsof the secondary winding from one transformer phase together up to thefurnace and forming the delta connection near the electrodes or in theelectrodes. If at the same time the three electrodes are placed in thecorners of a regular triangle the dead phase will be completely avoided,as previously known. In contradistinction to said delta connection,

I employa star connection on the secondary side and by specialarrangement of the secondary leads attain very low inductive voltagedrops. Heretofore the three electrodes were generally placed in oneplane and the neutral point of the star connection was either formed atthe transformers or at to the electrode began. If one three-phasetransformer was used the neutral point of the connection was generallyformed in the transformer and the three groups of leads from the threephases were in unison taken up to the furnace but again separated wherethe solid leads ended and the flexible leads began.

I place the electrodes in a triangle and take the leads up to theelectrodes in such manner that the leads are compensated, that is notsurrounded by any detrimental electromagnetic fleld, until they havepassed the electrodes or reached a point within a circle through thethree electrodes. The neutral point of the star connection may be formedeither at a point within a circle through the three electrodes or in thetransformer.

In the appended drawing Fig. 1 and Fig. 2 show a star connection withthe neutral point in the axis of the furnace. The leads to. the neutralpoint are somewhat thiimer drawn than the leads to the electrodes. M

Fig. 3 shows the neutral point formed at the transformer.

v 0n the primary side the transformers are delta connected. In all threeflgures l designates the transformers, 2 the furnace and 3 theelectrodes.

' As is known the secondary windings of big melting transformers aredivided into a series of parthe furnace where the flexible leads allelcoils, for instance eight. If the neutral point is not formed in thetransformer eight lead and eight return bars of the secondary windingwill leave the transformer cover. The current is best led to the furnaceby means of water cooled copper pipes. According to Fig. 1 two groups ofpipes from each phase lead to the corresponding electrode. Here thegroups separate; the flexible leads pass on each side ofthe electrode upto the electrode holder and the rigid pipes are led to the neutral pointwithin a circle through the electrodes.

each other in two vertical planes the power fields of the leads arecompensated all the way to the electrodes. Only the short pieces of theleads passing beyond the electrodesto the point within a circle throughthe electrodes remain non-compensated.- Fig. 2 shows a current supplywith the lead and return bars of the secondary winding in each phasecarried all the way to the axis of the furnace from where the flexibleleads go back to the electrodes, Fig. 3 shows a urrent supply which alsohas avery low inductive voltage drop and which only needs half thecopper cross section required for an arrangement according to Fig. 2.The neutral point is formed in the transformer and the individualconductors of the three phases are carried all the way to the pointwithin the circle through the electrodes. If, for instance, there areeight coils on each transformer core there will be a total oftwenty-four copper pipes, eight from each phase, which are led to thefurnace as close to each other as possible.

The pipes may be arranged in triangular position to avoid anytransmitting of energy from one exterior phase to the other.

Near the axis of the furnace the phases are separated and the copperpipes are connected As there are equal num-' bers of lead and returnbars of the secondarybeabove the furnace they are made in the, form ofwater cooled cables, that is, theleadconsists of a core of fine-threadedand flexible cable surrounded by a flexible metal hose in which watercirculates.

The star connection used in all these arrangements possesses incomparison with delta connection the great advantage that eachindividual electrode may be given just the voltage required for themoment. During operation it is sought to keep the electrodes atpractically the same depth in the furnace andthe transformers aretherefore arranged for adjustment of volta during operation. In the caseof delta connection, however, all three transformers must operate withthe same voltage as otherwise internal neutralization currents throughthe transformers may be developed. When using star connection eachindividual transformer may be adjusted independently and thetransformers may thus supply the electrodes with difierent operatingvoltages.

I claim:

1. Arrangement of compensated current supply for electric multi-phasefurnaces with star connection and with the electrodes arranged inequilateral triangle, characterized by the fact that the three phasesare compensated all the way to a point within a. circle through theelectrodes.

2. Arrangement of compensated current Sup ply for electric multi-phasefurnaces with star connection and with electrodes arranged in an equi-lateral triangle and in which the lead and return bars of the secondarywinding are compensated all the way to the electrodes, characterized bythe fact that the return bars of the secondary winding pass theelectrodes to a neutral point within a circle through the electrodes.

3. Arrangement of compensated current supply as in claim 2 characterizedby the fact that the short uncompensated portions of the bars which leadto the neutral point are separated from each other as far as possible.

4. Arrangement of compensated current supply for electric multi-phasefurnaces with star connection and with electrodes arranged in anequi-lateral triangle, characterized by the 'fact that leads from thesecondary winding are com pensated to a point within a circle throughthe electrodes and uncompensated for a short distance from suchpoint tothe electrodes, the short uncompensated portions of the leads beingseparated from each other as far as possible.

' H. INGELSRUD.

